1. Field of the Invention
The present invention relates to a method for preparing a hydrocarbon mixture solvent containing specific components. More particularly, it relates to a method for preparing a non-pollution solvent which never or scarcely contains aromatic hydrocarbons having various problems of safety and the like but which nevertheless has a high dissolving power for a resin, a surface active agent or the like.
The solvents of the present invention can be used as various solvents for printing inks, above all, lithographic printing inks, for dry cleaning, for washing, for extraction, for paints and the like.
Dry cleaning can be defined as the cleaning of farrics in a substantially non-aqueous liquid medium (solvent). This process has evolved into a highly effective, low-cost and safe method of removing soils from all types of textiles.
2. Description of the Prior Art
Heretofore, petroleum solvents have been used as solvents for washing, stain removing, rubbers, paints, extraction, dry cleaning, printing inks and the like. This kind of petroleum solvent is composed of a petroleum fraction which is obtained merely by distillation in a suitable boiling range. Therefore, this solvent directly contains components derived from the petroleum which is the raw material, and thus aromatic hydrocarbons are also inevitably present therein in a perceptible amount.
For example, as solvents for a printing ink, particularly for a lithographic rotary printing ink, there have been employed various solvents having boiling points within the range of 230.degree. to 300.degree. C. Such a kind of typical solvent is a hydrocarbon solvent of a mineral oil type. This mineral oil solvent has problems. That is, the mineral oil usually contains 20 to 30% of aromatic components and therefore has the problem of toxicity. Further, since the mineral oil is a continuous product, its boiling range is extensive. In consequence, the mineral oil contains heavy components and is thus difficult to dry after printing.
Depending on the use application of the solvent, aromatic hydrocarbons such as benzene, toluene and xylene are added on purpose thereto.
On the grounds that aromatic hydrocarbons such as benzene, toluene and xylene have a bad influence on human bodies, their content has become regulated.
For example, the Specific Chemicals Trouble Preventing Regulations in an ordinance of the Labor Ministry in Japan put severe restrictions on materials in which the content of benzene is more than 1 vol %, and the Organic Solvent Toxication Preventing Regulations also puts restrictions on the handling of materials in which the total content of toluene and xylene is more than 5 wt %.
In America, compounds such as naphthalene and biphenyl are regulated under the Occupation Safety and Health Act (OSHA), and the duty of indicating that these compounds are used is also imposed.
For the purpose of solving the above-mentioned problems, for example, Japanese Patent Publication No. 2319/1984 discloses a method of producing a solvent for rubbers such as a rubber type volatile oil which is prepared from a by-product pyrolysis gasoline fraction by (a) hydrogenation, (b) solvent extraction for the removal of aromatics and (c) distillation. The product is naphthene-rich oil containing 1 vol % or less of benzene and 5 wt % or less of toluene and xylene and having an aniline point of 50.degree. C. or lower. The content of naphthenes present in the solvent is however so great that the latter is not always satisfactory in point of performance, odor and the like. In other words, various physical properties of such a solvent are unbalanced.
Further, in the field of solvents for printing inks, it has been attempted to mix some nontoxic paraffins with the solvent in order to eliminate similar problems, but in this case, still other problems are posed which are, for example, easy solidification of the paraffins at a low temperature (5.degree. to 7.degree. C.), difficulty of adjusting varnish fluidity and poor dissolving power of the solvent for a resin. Furthermore, the simultaneous employment of the paraffins and naphthenes has also be attempted. However, if the content of the naphthenes in the solvent is great, its dissolving power for a resin will be poorer than with aromatic hydrocarbons, and the gloss of printed matter will deteriorate disadvantageously.
In the field of the dry cleaning solvents, it has been attempted to use a petroleum fraction which is nucleus-hydrogenated. Therefore, there has been used the fraction in which the content of aromatic components decreased and that of naphthene components increased however, such a fraction is expensive since a two-step nucleus hydrogenation process is usually used in its manufacture. In addition, the thus obtained solvent has, for example, the drawback that its power to dissolve a detergent at a low temperature is low. That is, in the case of the dry cleaning at a cleaning temperature which is elevated, stains which have gelled at a low temperature will be softened with the temperature rise and will be easy to remove. Moreover, the viscosity and a surface tension of the solvent will drop and permeability and dissolving power thereof will build up. The adsorption of the chosen surface active agent (detergent) will be accelerated, so that the stains will be swelled and will be liable to separate off conveniently.
As is definite from the above, elevating the cleaning temperature is extremely advantageous from the viewpoint of a washing effect, but it inversely causes the disadvantages that the quality of fabrics themselves tends to change and that the fabrics swell, weaken and thus break easily.
For these reasons, it is required that the cleaning be achieved even at a lower temperature on condition that cleaning results are sufficient.
Particularly with regard to animal fibers such as wool and silk as well as synthetic fibers, damage increases and dye and pressure treating agents tend to come off along with the rise of washing temperature. Hence, in the usual dry cleaning, the solvent is used at a temperature of about 20.degree. to about 25.degree. C. without heating particularly.
As described above, however, when the conventional fraction prepared by the mere hydrogenation is used as the solvent, the latter has a low dissolving power to detergent inconveniently.